Tin-plate flowing apparatus



Aug. 7, 1945. M. P. VORE 2,381,323

TINPLA'IE FLOWING APPARATUS F'il'ed NOV. 1]., 1942 :1: t I a WITNESSES: I INVENTOR ///%M mum P Vore, 7

V L my ATTORNEY Patented Aug. 7, 1945 UNITED STATES PATENT OFFICE 2,381,323 TIN-PLATE FLOWING APPARATUS Milton P. Vore, Catonsville, Md, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pat, a corporation of Pennsylvania Application November 11, 1942, Serial No. 465,270

3 Claims.

My invention relates to high-power radio-frequency inductive heating apparatus, and it has particular relation to apparatus of this kind, having so much power that it is necessary, or desirable, for one reason oranother, to subdivide the energy into a number of separate oscillationgenerators, each feeding power to a. separatecoilportion of the induction heating coil.

metal, is caused to run, at a very'high rate of speed, through a tinning line, in which various operations are successively performed on the strip, including electrolytically tinplating it on both sides, quickly heating it to a temperature of 452 F., or slightly thereover, for the purpose of melting the tinplate and causing it to flow evenly and glossily over the surface of the steel to enhance its corrosion-resistant properties, as well as improving its appearance, subsequently quenching the strip, and performing various additional operations thereon, having nothing to do with the present invention, except that it is necessary to gauge the rate of heat-input into the strip to correspond to the large poundage of material which has to be heated per minute, preferably within as short a strip-length as is practically possible.

The most satisfactory method of heating such a fast-moving strip, and practically the only method of controllably introducing the necessary quantity of heat within an acceptably short length of the fast-moving strip, is the inductive heating method, in which the strip is passed axially through an inductive heating-coil which is supplied with a large amount of power from a high-capacity oscillator-tube generator-means In a typical tinplate-fiowing application of my invention, the inductive heating-coil receives many times as-much energy as is used by the largest radio broadcasting station in theUnited rality of coil-sections, for the inductive heatingcoil, and a. plurality of separate, complete, oscillation-generators, one for each coil-portion.

The plurality of coil-portions are axially spaced, so as to be operative upon the same work tobe heated, and preferably the axial space is made sufiicient so that there is not a very close coupling between adjacent coil-portions. Preferably, also,

the oscillation-generators are tuned to slightly different frequencies, so as still further to reduce the likelihood of coupling, or energy-feedback, betweenadiacent coil-portions. The reduced coupling between adjacent heating-coils, and hence between the output-circuits of two oscillators that would normally operate at slight- 1y different frequencies, prevents these oscillators from operating in step at some compromise frequency diiferent from the natural frequency of either one separately, as they would do if their output-circuits were strongly jcoupled. The result of such forced oscillation, at a compromise frequency, would be that the load on the anode of each oscillator-tube would have a reactive component which would cause excessive anode-loss and heat-generation under such circumstances of strong coupling, thus sharply reducing the amount of energy which could be handled by States. With such large energy-input into the inductive heating-coil, the problem of generateach tube. The reduced coupling between outof-tune oscillators prevents this excesswe heatgeneration at the anodes, and it also overcomes a tendency for one of the oscillators to hog the load because of its feedback-coupling.

With the foregoing and other objects in view, my invention consists in the apparatus, combinations, circuits, systems, parts and methods hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a simplified diagrammatic view of circuits and apparatus illustrative of my invention.

I have illustrated my invention as being applied to the rapid inductive heating of a rapidly moving tinplated steel strip I, which generally has a gauge of between 0.008 and 0.011 inch, with a width of the order of 28 to 36 inches, more or less, and which is moving, in the direction of its length, at a speed which may be of the order of a thousand feet per minute, more orless. This strip i. passes axially downwardly through an inductive heating coil 2, comprising a plurality of axially'sp'aced coil-portions or sections 3, d, 5, 6, l and 8. Each coil-portion comprises a plurality of turns of a suitably cooled conductor, wound in a single layer, and having flat coil-sides In which are spaced from the oppoergized by means of site flat surfaces of the strip l which is being heated.

The coil-portions 3, 4, 6, 8,1 and I are each ena separate oscillation-generator I3, l4, l5, ll, l1 and 18 respectively. Each oscillation-generator comprises one or more oscillator-tubes lil, which are illustrated, in their simplest form, as having a cathode 20, an anode 2i, and a grid or other control' means 22. The anode 2| is connected, through a blocking capacitor 22, to a tank-circuit which comprises a tankcapacitor 24, a tank-inductance 25, and the coilsection, such as the coil-portion 3, which is supplied with energy by that particular oscillationgenerator. The connection'between the platecircuit blocking-capacitor 23 and the tank-circuit is illustrated as being made at the junctionpoint 28 between the tank-capacitor 24 and the tank-inductance 25, while the other terminal of the tank-capacitor 24 is illustrated as being grounded, at 21. The cathode-circuit of the oscillator-tube is also grounded, as indicated at 28.

Feedback-energy is illustrated as being obtained from the tank-circuit, as by means of a secondary winding 29 which is inductively 0011-, pled to the tank-inductance 25, and which energizes the grid 22 of the oscillator-tube through a grid-leak resistance H which is shunted by a grid-capacitor 32.

Each of the oscillation-generators ll, l4, l5, l8, l1 and I8 is supplied with direc;-current power by having its anode 2i connected through a choke-coil 34, to the positive bus 35 of the plate-voltage supply. Thus the power-supply bus 4! and the grounded cathode-connections 28 constitute the power-supply buses and for all of the oscillation-generators l3, l4, l5, l6, I1 and II.

The power-supply back of the oscillatorbuses and is illustrated asbeing derived from a three-phase line 41 which supplies power, through a circuit breaker 42 and an induction regulator 42, to the primary winding 44 of a, stepup rectifier-transformer 45, which is illustrated as having two star-connected secondary windings 48 and 41, the star-points of which are joined by an interphase-transformer 48, the midpoint of which is grounded so as to constitute the negative bus of the oscillator power-source. The phase-terminals of the secondary windings and 41 are connected, through a plurality of rectifiers 4!. to the conductor which constitutes the positive bus The induction regulator 42 is capable of being rapidly adjusted so as to obtain preferably 100% voltage-regulation, so that the temperature to which the strip I is heated may be accurately controlled, as explained in the Stoltz-Baker application.

In operation, it will be observed that each of the oscillation-generators ll, l4, I5, it, 11 and 1 ll supplies high-frequency power to its own coilportion 2. 4, I, 4, 1 and 8 as the case may be. Because of the special exigencies of the use to which the oscillation-frequency power is being put, it is practically necessary to operate each oscillationgenerator at an abnormally high Q, or high ratio of wattless power, which is stored in the tank-cir; cult. to the actual power which is delivered to the work .to be heated. This is because it is necessary to be able to start up the apparatus, of course; and this starting'must necessarily be done when the steel strip is cold, at which time the generaimpossible to utilize two loosely coupled tuned circuits, with the air-coil couplings such as are commonly utilized in high-frequency circuits, because a very slight relative detuning of the two circuits, one with respect to the other, at such a high Q, will make it practically impossible to transfer any material amount of power from one circuit to the other. It is necessary, therefore, to include the inductive heating-coil in seriescircuit relation as an eflective part of the tankcircuit of its own oscillator, for controlling the oscillator-frequency, so that, when the inductance of the coil changes in accordance with the conditor may haves. Q 01 the order of 10, whereas,

when the strip is hot, the'Q may be as high as 30.

Because of the high Q of the generator, it is tion of the work, as in the change which is involved between initially starting the apparatus when the strip is cold, and thereafter operating the apparatus when the strip is hot, the frequency of the oscillation-generator will vary with the change in the effective reactance oi the heating-coil; this frequency-change being small, but, nevertheless, important, and in fact the diner-- ence between being able to get the power into the strip and not being able to do so, in many cases.

Thus, it will be noted that each of the coilportions of the inductive heating-coil 2 is serially included as a part of the inductance of the tankcircuit of its own oscillation-generator, so that any change in the heating-coil inductance will be reflected in a corresponding change in the tuning of the generator. In this manner, I am able to pass from cold-strip operating-conditions to hot-strip operating-conditions, and I am also able to handle strips which are not always of the same uniform gauge or thickness.

The inclusion of the heating-coil 2 as a series portion of the tank-circuit has the advantage of being the simplest scheme and also having more efllcient energy-transfer than is feasible with any sort of link-coupling scheme, regardless of the Q of the tankcircuit.

The several tank-circuits of the respective oscillation-generators l3, 14, I5, ll, l1 and II are not all tuned to each other, which is another way of saying that they will not all be of the same frequency. Thus, if the general operatingirequency is of the order of 200 kilocycles per second, the individual frequencies of the separate oscillation-generators may vary, for example, between kilocycles and 210 kilocycles, more or less. The successive coil-portions 3, 4, I, 8, 1 and l are. physically separated from each other, in an axial direction, along the length of the strip I, by a distance which may be of the order of a root, or other distance such that the axially flowing fluxes in the successive coils have become considerably attenuated before successive coilsections are reached, thus considerably reducing the amount of coupling between the several coilsections. Thus, none of the oscillation-generators is materially aifected by the loosely coupled circuits of slightly different frequencies, which are loosely coupled by the several axially spaced heating-coils l to 8. This reduced coupling between the heating-coils prevents the excessive anode-losses that would otherwise be encountered in the tubes, and it also avoids the tendency for one oscillation-generator to take more than its share of the total load, as previously explained. While I have illustrated my invention in a single illustrative form of invention. ,Which has been shown in substantially its simplest, idealiaed form, I wish it to be understood that the usual features and safeguards, such as are commonly understood in the art, will be employed, without departing from my invention, and in variable ture of the member being heated, and, hence the fact as a part of any actual embodiment of my invention. For example, all of the conductors which carry radio-frequency power should be suitably cooled, as is well understood in the art, usually by means of water-cooling (nfit shown); I wish it to be understood, alswthat various changes, by way'of substitutions, additions, and omissions, may be made, without departing from the essential features of my invention. I desire, therefrom, that the appended claims shall be accorded the broadest construction consistent with their lansu se'and the prior art.

I claim as my invention:

1. Induction-heating apparatus for inducti heating an elongated member which is continuously moving in the direction of its length, said induction-heating apparatus comprising a plurality of spaced, coaxial induction-heating coils, following one another along a line to correspond to the length of the elongated memher, the magnetic coupling between successive induction-heating'coils being weak, a separate oscillation-generator means for separately energizing each induction-heating coil with oscillation-frequency energy, each oscillation-generator means having a tank-circuit effectively serially including its own induction-heating coil, the

inductance of each induction-heating coil being in accordance with the condition or nafrequenoy of each oscillation-generator tank-circuit being correspondingly variable, the ratio Q,

accuses diifere'ntfrequencies, whereby the several oscillation generator means are operable, each at its own frequency, substantially independently of the frequency of the other oscillation-generator means, thus avoiding excessive internal overheating as aresult of the reactive components of the currents in the several oscillation-generator means, and also avoiding any excessive tendency for any one oscillation-generator means to hog the load because of its feed-back. coupling.

2. The invention as defined in claim 1, characterized by' the several oscillation-generator means having all about the same frequency, with suiiicient differences to prevent substantial coupling'through adjacent induction-heating coils.

3. The invention as defined in claim 1, in coma bination with a common, variable-voltage, directcurrent supply-means for energizing all of the oscillationqzenerator means.

. MILTON P. VORE. 

